As is known, lead (Pb) is included in many conventional solder alloys. Further, an increasing number of microelectronic devices are prepared by a process using the aforementioned alloys. For environmental reasons, many countries are planning to mandate the exclusion of lead in soldering and other processes at some near future date. Therefore, it is highly desirous to provide a solder alloy free of such lead.
Accordingly, several kinds of lead-free solders are now being developed. These lead-free solders, however, are typically difficult to be effectively used in most manufacturing processes, due primarily to low wettabilities and higher melting points than known (tin-lead) solder alloys.
Various solder alloy compositions, including lead-free types, and processes using same are described in the following patents:
4,806,3095,368,8145,604,8314,929,4235,393,4895,730,9325,328,6605,411,7035,763,8545,344,6075,414,3035,866,0445,897,336
In addition to the foregoing, a method other than a gas atomizing method is described in Laid-Open Japanese Patent Publication No. 3-169500, wherein powder material of predetermined composition and small balls are put in a pot, which is then filled with inactive gas, sealed and rotated. The powder material is mechanically milled by the small balls. This method is mainly used to impart heat-resistance and thermal durability to solder powder material by mixing intermetallic compounds having high melting point with Sn—Pb alloy to make solder powder material. The method is acceptable in that it can prevent the solder powder material from forming large grains and that it does not require heat to melt the powder material during the preparation.
Recently, the use of intermetallic compounds in microelectronic products and processes having high melting points in turn appear to necessitate the use of solder alloy including lead. The aforementioned disadvantages caused by lead cannot be avoided, so it seems, when manufacturing such products. As will be defined hereinbelow, a solder powder material essentially free of lead has been developed which can be effectively used in a manufacturing environment, including particularly one wherein microelectronic products are made. Such a solder possesses both high wettability and a low melting point. It is believed that such a solder will constitute a significant advancement in the art.